Verificación de la Ley de Hess

Confirmación de que la entalpía es una función de estado usando tres reacciones

Thermochemistry Advanced (University) 60 min ~$15,00

Objetivo

Verificar la ley de Hess midiendo los cambios de entalpía de tres reacciones relacionadas y mostrando que ΔH₁ + ΔH₂ = ΔH₃.

Antecedentes

Hess's law states that the total enthalpy change for a reaction is independent of the pathway. This is verified by measuring: (1) NaOH(s) → NaOH(aq), (2) NaOH(aq) + HCl(aq) → NaCl(aq), and (3) NaOH(s) + HCl(aq) → NaCl(aq). The sum ΔH1 + ΔH2 should equal ΔH3.

Advertencias de seguridad

  • NaOH pellets are extremely corrosive and generate heat when dissolved
  • HCl is corrosive
  • Wear goggles and gloves throughout

EPP requerido

goggles gloves lab_coat

Materiales

  • Sodium hydroxide pellets (8 g)
    Anhydrous
  • Hydrochloric acid (HCl) (150 mL)
    1M
  • Sodium hydroxide solution (50 mL)
    1M
  • Distilled water (200 mL)

Equipamiento

Polystyrene cup calorimeter (2 cups nested) Thermometer Analytical balance Graduated cylinder Stopwatch Lid with hole

Procedimiento

1

Reaction 1: Add 50 mL distilled water to the calorimeter. Record temperature. Add 2 g NaOH pellets. Stir and record max temperature.

8 min Exothermic — NaOH dissolving
2

Calculate ΔH1 for dissolution. Repeat for accuracy.

5 min
3

Reaction 2: Add 50 mL 1M HCl to the calorimeter. Record temperature. Add 50 mL 1M NaOH. Record max temperature.

8 min
4

Calculate ΔH2 for neutralization.

5 min
5

Reaction 3: Add 50 mL 1M HCl to the calorimeter. Record temperature. Add 2 g NaOH pellets directly. Record max temperature.

8 min Very exothermic
6

Calculate ΔH3 for combined dissolution + neutralization.

5 min
7

Compare ΔH1 + ΔH2 with ΔH3. They should be approximately equal, verifying Hess's law.

8 min

Resultados esperados

ΔH1 (dissolution) ≈ -44 kJ/mol, ΔH2 (neutralization) ≈ -57 kJ/mol, ΔH3 (combined) ≈ -101 kJ/mol. ΔH1 + ΔH2 should equal ΔH3 within experimental error (±10%).

Limpieza

Neutralize all solutions before disposal. Rinse calorimeter cups. Dry and store equipment.

Detalles

Categoría
Thermochemistry
Dificultad
Advanced (University)
Duración
60 min
Costo estimado
$15,00
Pasos
7
Materiales
4

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Frequently Asked Questions

What is the objective of Verificación de la Ley de Hess?
Verificar la ley de Hess midiendo los cambios de entalpía de tres reacciones relacionadas y mostrando que ΔH₁ + ΔH₂ = ΔH₃.
How difficult is Verificación de la Ley de Hess?
This experiment is rated as Advanced (University). It takes approximately 60 minutes to complete.
What safety precautions are needed for Verificación de la Ley de Hess?
Key safety precautions include: NaOH pellets are extremely corrosive and generate heat when dissolved; HCl is corrosive; Wear goggles and gloves throughout.
What materials are needed for Verificación de la Ley de Hess?
The main materials required are: Sodium hydroxide pellets, Hydrochloric acid (HCl), Sodium hydroxide solution, Distilled water.
What results should I expect from Verificación de la Ley de Hess?
ΔH1 (dissolution) ≈ -44 kJ/mol, ΔH2 (neutralization) ≈ -57 kJ/mol, ΔH3 (combined) ≈ -101 kJ/mol. ΔH1 + ΔH2 should equal ΔH3 within experimental error (±10%).